Circuit breakers are well-known and commonly used to provide automatic circuit interruption to a monitored circuit when undesired overcurrent conditions occur. Some of these overcurrent conditions include, but are not limited to, overload conditions, ground faults, and short-circuit conditions. The component that senses and switches the circuit breaker to a TRIPPED position, i.e., a position in which the flow of current through the circuit breaker is interrupted, is a trip assembly. The trip assembly uses, in general, a spring-biased latch mechanism to force a movable contact away from a stationary contact.
Generally, a trip assembly includes a magnetic yoke, a movable armature, and a trip bar, which includes at least one trip finger. The movable armature is positioned such that a predetermined distance, a magnetic gap, exists between the movable armature and the magnetic yoke. The magnetic gap can be used to determine the current level required to trip the circuit breaker. For example, assuming that all other conditions are the same, a higher magnetic gap will require a higher level of current for tripping the circuit breaker, while a lower magnetic gap will require a lower level of current for tripping the circuit breaker. When the current level rises above a predetermined level, a magnetic force is generated through the magnetic yoke and the movable armature is magnetically attracted towards the magnetic yoke. During its motion toward the magnetic yoke, the movable armature comes in contact with the trip finger and actuates the trip bar, which in turn switches the circuit breaker to the TRIPPED position.
In one type of trip assembly, used in a calibrating circuit breaker, the movable armature is connected to the trip bar using a spring, which has one end directly connected to the movable armature and one end connected to the trip bar via a calibration screw. Because of manufacturing defects, the magnetic gap generally varies from pole to pole and, consequently, each pole of a circuit breaker must be individually calibrated. By adjusting the screw, which results in either increasing or decreasing the magnetic gap, each pole of the circuit breaker can be calibrated to perform as intended.
One problem associated with this type of trip assembly is that each of the circuit breaker poles must undergo a calibration process before installation, a process that is expensive and time-consuming. Additionally, some circuit breakers have to go through a recalibration process after installation, a process that increases the cost and decreases the productivity associated with the use of the circuit breakers. Eliminating the calibration process and the recalibration process associated with the manufacturing and the use of circuit breakers would result in decreased costs and increased productivity. The present invention exploits these and other advantages.